The administration of tumor specific antibodies which possess chemotactic activity might enhance tumoricidal host defense by directing the migration of inflammatory cells to a tumor site. The synthetic chemotactic peptide formyl-methionyl-leucyl-phenylalanine (f-MLP), has been covalently coupled to rabbit antibodies specific for a strain 13 guinea pig hepatoma. The tumor specific antibodies coupled to f-MLP (chemotactic antibody) retain their antigen binding properties and, in addition, are chemotactic for guinea pig peritoneal exudate cells. However, the "chemotactic antibodies" are relatively ineffective in inducing complement dependent cytotoxicity (CDC). The coupled antibodies are also chemotactic when bound to the tumor cells, implying that the antibodies, antibody-tumor antigen complexes or the f-MLP may be released and establish an effective chemotactic gradient for peritoneal exudate cells. These findings suggest that in vivo the chemotactic antibodies may localize in a tumor site where they would initiate the influx of inflammatory cells.